The painting operation when repairing a vehicle includes a process for drying the paint applied to the vehicle body. Usually, in this process, there is used an infrared drying apparatus which dries the painted surface by irradiating it with infrared rays, a hot air drying apparatus which dries the painted surface by blowing hot air against the painted surface or the like, achieving a reduction in operation time by forcibly drying the painted surface.
According to studies of the present inventors, etc., it has been found out that in order to efficiently dry the painted surface, the following conditions must be satisfied. A first condition is to quickly evaporate the solvent contained in the paint from the inside. A second condition is to quickly dissipate from the painted surface the solvent evaporated from the inside of the paint. A third condition is to quickly polymerize pigment, which is the main component of the paint. It has been found out that by satisfying such conditions, the drying time can be substantially shortened. It has also been found out that by satisfying these conditions, at the same time, it is possible to obtain a satisfactory painted surface free from defective drying.
Examples of defective drying include pin holes generated by insufficient degassing of the solvent and blister. The pin holes are referred to as voids generated in the painted surface by evaporation of the solvent remaining in the paint through breaking the coating film formed on the painted surface, when the film is formed on the surface in a state where degassing of the solvent is insufficient. Blister means local swelling of the painted surface as a result of bonding of the solvent remaining in the coating film with the water in the air after completing the drying of the painted surface.
However, the conventional drying apparatuses do not satisfy the above conditions to a sufficient degree. That is, in the infrared drying apparatus, drying (heating) is started from the inner side of the painted surface by infrared rays emitted from the apparatus. The solvent evaporated from the inside of the paint, however, remains on the painted surface in a calm state. Thus, evaporation of the subsequent solvent is hindered by the remaining solvent.
In the hot air drying apparatus, drying (curing) is started from the painted surface by hot air sent from the apparatus. Thus, prior to evaporation of the solvent contained in the paint, a coating film (drying film) is formed on the painted surface. Thus, evaporation of the solvent in the paint is hindered by the coating film (drying film) formed prior to the evaporation of the solvent.
In some hot air drying apparatuses, infrared rays are emitted when generating hot air. However, the contribution of the infrared rays to the drying of the painted surface is negligible as compared with that of the hot air. Thus, drying performed from the inner side of the painted surface by infrared rays is not to be expected.